Electrostatic spray nozzles with multiple outlets are fairly well known in the art, and in most of the conventional devices, all of the individual outlet ports are of the same length. This uniform length, however, does not cause a uniform electric field to exist at the tips of the individual outlet ports, which thereby causes different spraying patterns to occur for different outlet ports. Since all of the tips are at the same high voltage value, they tend to interfere with one another with regard to the magnitude and direction of the electric fields at those very same tips.
In U.S. Patent Application Publication No. U.S. 2002/0007869 A1 (to Pui) the nozzle lengths have been varied, however, the distances between each of the tips for the nozzle outlet ports and the target surface has remained the same. This relationship can be seen in FIG. 5A of Pui. The main objective of Pui is to spray charged particles (or droplets) onto a targeted surface, regardless of the size of the outlet port diameters of the individual nozzles, and regardless of the size of the droplets that are produced by those outlet ports. This type of arrangement is not suitable for an “air cleaning” application, in which the charged spray droplets are meant to produce a spray cloud within a predetermined space to remove particulate matter from a stream of “dirty” air.
In the conventional nozzle spraying systems, the charging voltage is a single value for all of the individual nozzles, and since the distance between the individual nozzle outlet ports and the target surface is essentially equal for all nozzles, the electric field strength at the tips of each of the individual nozzles will not be constant due to the proximity of one charged nozzle to the next. Therefore, the individual nozzles will not spray in a uniform manner (from one nozzle to the next). Instead, the spray patterns will vary, mainly depending upon the actual electric field magnitude at each of the nozzles. In general, some of the inner nozzles will exhibit an electric field magnitude that is much lower than the electric field magnitude at some of the outer nozzles; the lower field strength nozzles will produce smaller, and probably less well dispersed, spray patterns.
It would be an improvement to build a multiple-outlet port electrostatic nozzle that provides a more uniform, or a substantially uniform, electric field at each of the outlet port tips.